A liquid crystal panel itself does not emit light, thus, a backlight is required to be placed behind the liquid crystal panel. The liquid crystal panel and the backlight are fixed by a mechanical structure. In a normally white liquid crystal panel, when an electric field is applied on liquid crystal molecules, the liquid crystal panel may block the spread of light, so that a totally black screen is displayed. In a normally black liquid crystal panel, when no electric field is applied on the liquid crystal molecules, the liquid crystal panel may block the spread of light, so that the totally black screen is displayed.
However, under normal circumstances, especially in an advanced super dimension switch (ADS) mode liquid crystal panel, the liquid crystal panel is not able to completely block the light. Particularly at a mechanical engagement structure on edges of the panel, since a front frame on the edges of the liquid crystal panel is usually manufactured by die stamping which is not a precision machining, thus, it is difficult to ensure good flatness and small dimensional tolerance. Further, even using a front frame with good flatness, the front frame may be deformed during a process of assembling a liquid crystal display module, resulting in that a gap between the front frame and the liquid crystal panel becomes smaller. Therefore, compressive stress against the liquid crystal panel caused by a deformed portion of the front frame becomes larger, thereby significantly weakening effects of blocking the light by the liquid crystal panel, and a light-leakage phenomenon appears in the totally black screen.